The present invention relates to signal acquisition, and more particularly to real-time acquisition of RF signals.
Some instruments, such as spectrum analyzers, capture and process received RF signal in real time. For example there currently are several spectrum analyzers on the market, such as the Tektronix WCA200, WCA300, RSA2200 and RSA3300 series real-time spectrum analyzers manufactured by Tektronix, Inc. of Beaverton, Oreg., that capture and analyze seamless blocks of data. Unlike conventional frequency swept spectrum analyzers, no data is missed or lost by these real-time instruments. One function that is performed in real time is called a frequency mask trigger, as described in U.S. Pat. No. 5,103,402. The frequency mask trigger may be implemented with a dedicated fast Fourier transform (FFT) processor that calculates the signal spectrum on the real-time data provided by a receiver system in the real-time instrument. When the calculated spectrum violates a user-defined spectrum (frequency) mask, a predefined block of data representing the received RF signal is stored that provides information on what happened immediately prior and/or after the triggering event. The frequency mask trigger works by comparing each FFT frequency bin in the calculated spectrum with a predefined spectral mask. In this way the frequency mask trigger waits for a specific single spectral event to occur.
More conventional triggers, as in oscilloscopes, operate in the time domain by comparing an input signal amplitude to a predefined amplitude threshold or thresholds, for example. However these “one-dimensional” trigger systems are not adequate to capture complicated signal events. As a result in oscilloscopes complicated time domain trigger functions have been implemented to trigger on different types of signal events.
What is desired is to extend the domain of real-time triggering beyond frequency mask triggering or conventional time-domain (amplitude) triggering to capture more complicated signal events.